Many modern communication networks are adapted to detect and react to defects that may impair the transmission of data along such networks. Synchronous optical networks (“SONET”), for example, detect network defects and switch the routing of traffic within the network along differing physical paths in the presence of a defect, to ensure data traffic delivery between end points. Such switching is typically referred to as “protection switching”.
Modern ATM networks, as for example detailed in International Telecommunication Union Recommendations ITU-T I.326, I.610, I.630, and I.732, the contents of all of which are hereby incorporated by reference, support similar protection switching in the presence of defects to provide a signal across the network in the presence of signal failure (signal fail—“SF”), or in the presence of a degraded signal (signal degrade—“SD”). SF is often manifested in loss of frames (LOF); loss of signal (LOS); or loss of cell delineation (LCD) at the physical layer carrying ATM traffic. As such ITU-T Recommendation I.630, suggests that a SF may be detected at the physical layer. SD, on the other hand, typically manifests itself in the presence of bit errors within the ATM signal. As such, ITU-T Recommendation I.630 suggests detecting SD at the ATM layer, by using performance monitoring (“PM”) flows.
As should be appreciated, as the ATM layer relies upon the existing physical layer, faults detected at the ATM layer of the network are often detected some time after the same fault manifests itself at the physical layer. As such, the ATM layer is currently unable to detect and react to a SD condition as quickly as the physical layer might detect signs of the SD.
Accordingly, a method and apparatus that facilitates ATM layer protection switching with the speed of defect detection of the physical layer in the presence of SD is desirable.